The background description provided herein is for the purpose of generally presenting the context of the disclosure.
Diesel engines combust fuel in the presence of air to produce power. The combustion of fuel produces exhaust gas that contains particulate matter (PM). The PM may be filtered from the exhaust gas using a PM filter. Over time, the PM may accumulate within the PM filter and may restrict the flow of exhaust gas through the PM filter. PM that has collected within the PM filter may be removed by a process referred to as regeneration. During regeneration, PM within the PM filter may be combusted.
Regeneration may involve heating the PM filter to a combustion temperature of the PM. There are various ways to perform regeneration including modifying engine management, using a fuel burner, using a catalytic oxidizer to increase the exhaust temperature with after injection of fuel, using resistive heating coils, and/or using microwave energy.
Diesel PM combusts when temperatures above a combustion temperature such as 600° C. are attained. The start of combustion causes a further increase in temperature. Once the PM is ignited, the burning PM may be used to regenerate the rest of the filter. In other words, cascading flame front moves from the inlet to the outlet of the PM filter. While spark-ignited engines typically have low oxygen levels in the exhaust gas stream, diesel engines have significantly higher oxygen levels. While the increased oxygen levels make fast regeneration of the PM filter possible, it may also pose some problems.
Referring now to FIG. 1, a PM filter system 10 for regenerating a PM filter is shown. The PM filter system 10 includes a heater 12. The PM filter system 10 further includes a particular matter filter 14 that includes walls 16-1, 16-2, . . . , and 16-6 (collectively walls 16). Some pairs of the adjacent walls 16 define outlet channels and may include an inlet end plug. Other pairs of adjacent walls define inlet channels and may include an outlet end plug.
In particular, adjacent walls 16-1 and 16-2, 16-3 and 16-4, and 16-5 and 16-6 define outlet channels and include an inlet end plugs 18-1, 18-2, and 18-3, respectively (collectively inlet end plugs 18). Adjacent walls 16-2 and 16-3, 16-4 and 16-5 include define inlet channels and include outlet end plugs 20-1 and 20-2, respectively (collectively outlet end plugs 20).
In use, exhaust flows through the heater 12 and into inlet channels of the filter 14. The exhaust flows from the inlet channels through the walls 16 into adjacent outlet channels. PM is filtered as the exhaust gas passes through the walls 16 and builds up on the walls 16 in the inlet channels. PM also builds up in the inlet channels in areas around the outlet end plugs 20.
Referring now to FIGS. 2-4, regeneration within the PM filter system 10 is shown. In FIG. 2, when the heater 12 is turned on, PM adjacent to the heater begins burning in a burning zone. The substrate temperature in areas beyond the burning zone may be less than the PM ignition temperature. Therefore, there is no regeneration in these areas at this time.
In FIG. 3, the burning zone moves along the length of the PM filter 14. Regeneration of the PM continues as long as the burning zone temperature is above the PM ignition temperature. In FIG. 4, if the burning zone temperature falls below the PM ignition temperature, the filter 14 will not be regenerated fully. In other words, PM may remain in portions of the filter 14 that are adjacent to the outlet end plugs 20.
To avoid this situation, the heater 12 may be turned on to heat the PM filter to a higher initial temperature. The higher temperatures may tend to decrease the durability of the PM filter.